Hydraulic work machines, in particular mobile machines such as wheel loaders, tractors, scrapers, graders, and the like, are used extensively to perform work functions such as altering terrain, moving material, constructing roads, lots, runways, and repairing the same. Generally these hydraulic work machines have a power source, i.e., an engine, to move about, and this same power source is also used to power the hydraulic systems on the machine.
Occasionally, an engine will malfunction on a machine, thus disabling the machine from moving about, and also disabling the hydraulic systems. It is common for such a machine to use a spring applied, hydraulic pressure released brake system; that is, the brakes are always engaged by spring action until controlled hydraulic pressure to the brakes overcomes the spring force and releases the brakes. In a dead engine situation, the brakes will be engaged. If the machine is required to be towed, some means is needed to release the brakes for towing.
Several patents exist which disclose methods for releasing brakes for towing under dead engine conditions. For example, in U.S. Pat. No. 4,195,716, Wirt discloses a brake release mechanism for vehicle towing which uses a manual hydraulic pump means to manually pump fluid into the brake system and thus disengage the brakes for towing. Although the system disclosed by Wirt accomplishes the purpose of releasing the brakes, some significant effort is required by a human to perform this procedure. What is needed is a means to release the brakes for towing while minimizing the human effort required.
In addition to the need to release the brakes for towing under dead engine conditions, it often occurs that a work implement is in contact with the ground when the engine fails. In this situation, the implement would need to be raised above the ground to prepare the machine for towing. The hydraulic pressure required to raise an implement, particularly a heavy implement or an implement with a heavy load, would be tremendous. For example, a compactor/hammer mounted on a wheel loader may weigh in excess of 14,000 kg. Historically, an implement is raised for towing by either manually pumping hydraulic fluid into lift cylinders or by connecting a pump from a service vehicle to the disabled work machine and then pumping hydraulic fluid into the lift cylinders. In either case, it is desired to enable lifting of an implement for towing by some convenient means located within easy access to an operator, and without requiring the manual connection of some other system.
The present invention is directed to overcoming one or more of the problems as set forth above.